From 7880d870919d58b751f6bc47669052b45eb9db30 Mon Sep 17 00:00:00 2001
From: Alexander Slobodeniuk <aslobodeniuk@fluendo.com>
Date: Fri, 3 Nov 2023 17:00:11 +0100
Subject: [PATCH] gvalue: add g_value_steal_string()

This call is needed to avoid an extra copy after
serialization of the data.
---
 docs/reference/gobject/gobject-sections.txt |  1 +
 gobject/gvaluetypes.c                       | 35 +++++++++++++++++++++
 gobject/gvaluetypes.h                       |  2 ++
 gobject/tests/value.c                       | 23 +++++++++++++-
 4 files changed, 60 insertions(+), 1 deletion(-)

diff --git a/docs/reference/gobject/gobject-sections.txt b/docs/reference/gobject/gobject-sections.txt
index cf06cf183..3f7f67386 100644
--- a/docs/reference/gobject/gobject-sections.txt
+++ b/docs/reference/gobject/gobject-sections.txt
@@ -719,6 +719,7 @@ g_value_take_string
 g_value_set_string_take_ownership
 g_value_get_string
 g_value_dup_string
+g_value_steal_string
 g_value_set_interned_string
 
 <SUBSECTION GParamSpec>
diff --git a/gobject/gvaluetypes.c b/gobject/gvaluetypes.c
index 6ffa7fd8b..6ed6d9cce 100644
--- a/gobject/gvaluetypes.c
+++ b/gobject/gvaluetypes.c
@@ -1159,6 +1159,41 @@ g_value_dup_string (const GValue *value)
   return g_strdup (value->data[0].v_pointer);
 }
 
+/**
+ * g_value_steal_string:
+ * @value: a valid #GValue of type %G_TYPE_STRING
+ *
+ * Steal ownership on contents of a %G_TYPE_STRING #GValue.
+ * As a result of this operation the value's contents will be reset to %NULL.
+ *
+ * The purpose of this call is to provide a way to avoid an extra copy
+ * when some object have been serialized into string through #GValue API.
+ *
+ * NOTE: for safety and compatibility purposes, if #GValue contains
+ * static string, or an interned one, this function will return a copy
+ * of the string. Otherwise the transfer notation would be ambiguous.
+ *
+ * Returns: (nullable) (transfer full): string content of @value;
+ *  Should be freed with g_free() when no longer needed.
+ *
+ * Since: 2.80
+ */
+gchar*
+g_value_steal_string (GValue *value)
+{
+  gchar *ret;
+
+  g_return_val_if_fail (G_VALUE_HOLDS_STRING (value), NULL);
+
+  ret = value->data[0].v_pointer;
+  value->data[0].v_pointer = NULL;
+
+  if (value->data[1].v_uint & G_VALUE_NOCOPY_CONTENTS)
+    return g_strdup (ret);
+
+  return ret;
+}
+
 /**
  * g_value_set_pointer:
  * @value: a valid #GValue of %G_TYPE_POINTER
diff --git a/gobject/gvaluetypes.h b/gobject/gvaluetypes.h
index 0c8d0f66e..afa659530 100644
--- a/gobject/gvaluetypes.h
+++ b/gobject/gvaluetypes.h
@@ -263,6 +263,8 @@ GOBJECT_AVAILABLE_IN_ALL
 const gchar *         g_value_get_string	(const GValue *value);
 GOBJECT_AVAILABLE_IN_ALL
 gchar*		      g_value_dup_string	(const GValue *value);
+GOBJECT_AVAILABLE_IN_2_80
+gchar*		      g_value_steal_string	(GValue *value);
 GOBJECT_AVAILABLE_IN_ALL
 void		      g_value_set_pointer	(GValue	      *value,
 						 gpointer      v_pointer);
diff --git a/gobject/tests/value.c b/gobject/tests/value.c
index 73a5de650..d1a90919a 100644
--- a/gobject/tests/value.c
+++ b/gobject/tests/value.c
@@ -420,7 +420,7 @@ test_value_string (void)
   const gchar *static2 = "static2";
   const gchar *storedstr;
   const gchar *copystr;
-  gchar *str1, *str2;
+  gchar *str1, *str2, *stolen_str;
   GValue value = G_VALUE_INIT;
   GValue copy = G_VALUE_INIT;
 
@@ -513,7 +513,12 @@ test_value_string (void)
   g_assert_true (storedstr != static2);
   g_assert_cmpstr (storedstr, ==, static2);
 
+  /* Now check stealing the ownership of the contents */
+  stolen_str = g_value_steal_string (&value);
+  g_assert_null (g_value_get_string (&value));
   g_value_unset (&value);
+  g_assert_cmpstr (stolen_str, ==, static2);
+  g_free (stolen_str);
 
   /*
    * Static strings
@@ -544,6 +549,14 @@ test_value_string (void)
   g_assert_true (storedstr != static1);
   g_assert_cmpstr (storedstr, ==, static2);
 
+  /* Check if g_value_steal_string() can handle GValue
+   * with a static string */
+  stolen_str = g_value_steal_string (&value);
+  g_assert_true (stolen_str != static2);
+  g_assert_cmpstr (stolen_str, ==, static2);
+  g_assert_null (g_value_get_string (&value));
+  g_free (stolen_str);
+
   g_value_unset (&value);
 
   /*
@@ -588,6 +601,14 @@ test_value_string (void)
   g_assert_true (storedstr != static2);
   g_assert_cmpstr (storedstr, ==, static2);
 
+  /* Check if g_value_steal_string() can handle GValue
+   * with an interned string */
+  stolen_str = g_value_steal_string (&value);
+  g_assert_true (stolen_str != static2);
+  g_assert_cmpstr (stolen_str, ==, static2);
+  g_assert_null (g_value_get_string (&value));
+  g_free (stolen_str);
+
   g_value_unset (&value);
 }